The present invention relates to ultrasonic imaging and, more particularly, to a novel two-dimensional phased array of ultrasonic transducer.
In many ultrasonic imaging systems, for use in medical diagnostics and the like, an array of a plurality of independent transducers is formed to extent in a single dimension (say, the X-dimension of a Cartesian coordinate system) across the length of an aperture. The energy independently applied to each of the transducers is modulated (in amplitude, time, phase, frequency and the like parameters) to form an energy beam and electronically both steer and focus that beam in a plane passing through the elongated array dimension (e.g. an X-Z plane, where the Z direction is perpendicular to the array surface). However, in a transverse Y-Z plane the beam is actually focussed at only one distance as there is a fixed mechanical lens used to obtain focus in the direction orthogonal to the elongated dimension of the array. It is highly beneficial to be able to electronically variably focus the beam in both the X-Z and Y-Z planes, i.e. in the X and Y directions perpendicular to the beam pointing (generally, Z) direction. It is desired to provide the array with an electronically-controlled two-dimensional aperture in which each of the phased array dimensions has a different role. Thus, for a beam directed in a given, e.g. Z-axis, direction, beam control in a first, or X, orthogonal direction serves to both steer and focus the radiation, while beam control in an orthogonal second, or Y, direction is utilized for focussing the beam to a point at all locations to which the beam can be steered (which can not be accomplished by a one-dimensional array). Therefore, a desired transducer array emits a radiation pattern which had distinctly different characteristics in the (X or Y) directions orthogonal to the beam (Z) direction. It is, therefore, highly desirable to provide a two-dimensional ultrasonic phased array, formed of a plurality of transducers, having steering and focussing ability in a first direction and focussing ability in an orthogonal second direction.